Investigation on Oxidation of Shelf-Aged Crosslinked Ultra-High Molecular Weight Polyethylene (UHMWPE) and Its Effects on Wear Characteristics

Abstract

Oxidation degradation of gamma-irradiated UHMWPE (Ultra-high Molecular Weight Polyethylene) is a well-known problem related to the failure of total joint replacement. The purpose of this study is to investigate the effects of oxidation on the mechanical and wear properties and to identify the main causes of the change of wear mechanisms of crosslinked UHMWPE (50 kGy and 100 kGy) after long-term shelf-ageing. The techniques used were FTIR mapping and micro-indentation test, which were performed on the same cross-section of UHMWPE specimen. Three distinct regions (the surface region, the more oxidized subsurface region, and the less oxidized center region) were prepared to carry out the differential scanning calorimetry (DSC) and multi-directional wear tests. The worn surfaces were checked by optical microscopy and scanning electron microscopy to reveal the wear mechanisms. The experimental results showed that the micro-hardness, elastic modulus and crystallinity increased with the increase of the oxidation index. The wear resistance deteriorated when the oxidation index increased. The slope of specific wear rate against oxidation index of the 100 kGy sample is higher than that of the 50 kGy sample. Our results may indicate that, when the oxidation index is lower than the critical threshold, the wear mechanism is mainly dependent on crosslinking density; when the oxidation index is higher than the critical threshold, the oxidation behavior plays an important role in the change of wear mechanisms.

Keywords

• uhmwpe
• wear
• oxidation
• crosslinking
• gamma-irradiation
• shelf-ageing